In many types of motor-driven systems it is desirable to have an indication of the position of the load driven by the motor. Many such systems utilize a potentiometer whose wiper is driven by the motor or its load. The potentiometer is then connected into a feedback system, and its wiper voltage is used as an indication of the position of the motor or load. This type of arrangement is very inexpensive, but has certain problems relating to reliability.
The potentiometer driven by the motor or its load can provide an inaccurate signal under many different types of fault conditions. The potentiometer can become open circuited, its wiper can become disengaged from the potentiometer body by dirt or wear, or the potentiometer can become so worn as to provide an inaccurate feedback signal. In many types of systems the accuracy of the feedback signal is critical. In these types of situations other means in addition to a potentiometer feedback system are utilized.
Where safety is involved and the exact position of a load must be accurately reported to the system, means such as limit switches have been used. When the motor drives the load to a required position the switches are activated and their signal is returned to the control system. It is apparent that this type of arrangement has costs related to the need to mount the switches, and to add the wiring from the switches back to the control device.